Push-pull amplifier



Aug. 29, 1933- STRECKER 1,924,469

PUSH-PULL AMPLIFIER Filed Jan. 2, 1952 INVENTOR FEUX STRECKER BY Qmu/ATTORNEY Patented Aug. 29, 1933 v 1 j I i e UNITED; STATES PATENT:OFFICE;

PUSH-PULL AMrniF En Felix StreckerfBerlm, Germany, assignor to Siemens &Halske, Aktiengesellschaft, Siemensstadt, near -Berlin, .Germany, acorpora-V .tion of Germany Application January 2, 1932, SerialN6.;5s4,4o6,

and in Germany October 22, 1930 i V 1 Claim. (c1.- 179-171 The object ofthe invention is a push-pull ment, whereas the output transiormer Ua atits amplifier circuitscheme which, asregards sym primary end is unitedthrough condensers Q with metry of output currents, compared with thethe terminal points of the resistances and thus I arrangements known inthe earlier art, is. adapted withthe plateslA; In this manner thepotential. I r 5 to secure particularly high accuracy. I of theelectrCalmidpoint of the primary winding The arrangement here disclosedinsures such oftheltransformerlis fixed, theaccuracy'ofsymi great,symmetry that instead of'ithe customary netrylis governed by theaccuracy of the agreeoutput transformeror instead of a potential ment ofthetwo resistances 'r. When push-pull divider comprising inductancecoils, there is pro transformers are used, symmetry is governed by 10vided an arrangement of ohmic resistances to the accuracy of agreementof the'propertiesof which the output transformer is associated cathetwo. separatewindings ,(inductances, leak pacitively. ages,self-capacitance, etc) and thesame is The arrangement here disclosedoffers partherefore substantially less close. Y ticularly greatadvantages in connection with the, Furthermore the secondary endfof theinput '15 idea well known in the prior art of shunting "thetransformerUejis connected with aresist'ance By .70 7

input transformer bymeans of two series conby way of 'a condenjser Q,"the two, grids G1,

I nected similar ohmic resistances, the filaments and G2, beingconnected to the two terminals of being associatedjwith the midpoint ofthis series said resistance Ry. cathodes Kland K2 are arrangement,whereas the secondary end of the united with a point inside theresistance Rg,

20 input transformer is capacitively connected with and thisway also 1symmetry ofthe inputis inthe resistance, by virtue of such symmetricdissured' t0 ,,an,extensive extentif i position both at'the input andthe output ends Under the assumptionfthat both tubes as well of theamplifier the danger oi the arising vof as the balance of circuitelements'are perfectlyback-feeds is extensively precluded,contradistinct similar, a circuit scheme of this kind would be '25 fromwhat is trueto a mark ed degree where syn 1 m e r m r s nd, free from.pur 8 1 In the drawing two embodiments ofithe basic thetvvo branchcircuits betweenjk and the t 5 deserves special importance in thiscombination.

V59 gram.

metric conditions are 'securedonly at the input back-feds- W YC l fadefectsiand end. Quite apart from thereduction of ,the en at n a dduc d.owing to the fact chances of back-feedslbeing set up, an arranget t. P ry. the tu eney r bs ut y ment of the kind here disclosed ofier'sadvantages k V V 0 also in other respects. ,I n'the. presence 'offin-Accqlding q vfi t i h mil s .8 equality of the amplifier curves both asregards ay be obviated by suitable adjustment or fixing amplitude andphase, the two tubes, fail com- ,Qf he te mlnal foontacts upon the inputres'isf l operate in an accurate manner also as amplifiance Rgand Ontheoutput resistance r.'.= 2r.,,A' I fiers, most particularly, at the,,hppr ,frequen'cy circuit Scheme in wh c hE SQ .featureshavebeen j 35limit. In other words, the amplifier is then adapta ep da po ated isillustrated in Fig.2; ed only for the lowerfrequency ranges. The I thefi st place attentionlshall be drawn to use of resistances secures aconvenient equaliz'a the, advantages; obtained by 'Inakin'g,,,,-thetermi-v tion also in this regard, while this is quite diflicult. rial7:: or the plate potential vsourceBA shiftable. V where coils areemployed, upon the resistance r'., Theplate'currents, in

idea of the inventionfareillustrated by way of m t 1 and 2 lt i drops bf t ti l 750 examp these scbe isc m e is that the residual platepotentials are dependent the idea of rendering the input end symmetric.upon thepositiofi" t e Contact oft'erminal indeed, the fundamental, ideaof'this invention present some .dissymmetry or another which, if 1, ithe contact is f were set to the --exact midpoint of the resistancewould result in dissymmet'ric out put currents, then, by suitableselection of the Fig. lisabasic principle embodiment ofsuch anarrangement, while in Fig. 2 several particularly advantageousembodiments or construction- 9.1 features are shown ina detailed keydia- AS indicated i Fig L the plates A1 nd A venient adjustment of theslidable contact 70 of the two tubes R1 and R2 are inter-connected it ispossible o eliminate t said e t. se in by way of two similar ohmicresistances r. The that the outputaltfi Curmnt i a u ction platepotential source BA.iS associated to a tap of the .plate potential.Arrangement could also 55 is disposed at the midpointjof this seriesarrangebe made in such a way that potentials of differ: 0

-Now, -if"the circuit elements; especiallyv the tubes," 6

plate potential relation, in other words, by conent value for the twotubes are taken from the plate potential source.

Another mode of insuring regulation consists in balancing out suchdiscrepancies as may obtain in 'theinternal resistances of the two tubesby supplementary resistances T1 and T2. In this case the resistanceshunting the plates comprises three parts, to the middle one of whichthe primary of the output transformer Ua is united by way'of the twocondensers C andwhich has a constant value. The two outer sections T1and r2, on the contrary, may beiset to anydesired value in fact, theyserve for equalizing such discrepancies as may exist in'the' internalresistances .of-the tubes, 7

A similar idea could be usedwith referenceto the input end. vIn theexample illustrated in the Figure, two resistances'having different tapsare used, in fact, the contacts or connections for the grids G1 .andG2,those forthe filaments K1 andKZ and finally'also those for the secondarywinding of the. input transformer Ue are adjustable ad libitum. Thisembodiment further shows that the grid biasing potential for, both tubesis separately regulable. This disposition makes it possible toneutralize, particularly irregularities in the valueof 1: a of thetwotubes,

' (cross-grid actions of the plates) ,and the effects thereof. If in thepresence of aperfectly symmetric setting of the ohmic input resistancesboth.

tubes are fed with the same, alternating current potential, then theinequality of 1: 1, has this effect that the ensuing 'electromotiveforcesin M theplate circuits areunequal. This discrepancy,

however, could also be obviated by that the potentials supplied to thegrids are altered in this sensethat thedifierences thus caused willcompensate the differences in the values jof 1:

, The provision of different grid potentials (bias),

effect compensation from case to; case especially when this necessityarises owing to the substitution of a tube or tubes.

It will be obvious, that somesuchschemes of securing symmetry could 'beadopted also only for the input end, whilethis maybe dispensed with atthe output end, this condition being. particularly present where noohmic resistances 'are usedatthe' outpu't end. 5 The" samething,

of course, mightarisealso for the output'end. Another source of troubleresides in'capacitive dissymmetries. In order that these may be ob:

viated as far as feasible it is necessary that the circuit elementscomprised, in the two paralleled amplifier branches should be madesymmetric not only in electrical but also in spatial (geometric)respect, that is to say, to dispose them symmetrically not only inreference toeach other, but also in reference to the neighboringconductors. However, inasmuch as this is practically feasible onlyto acertain extent, inevitable ca-' pacitive dissymmetriescan be renderedharmless by capacitive equalization, as shown, for instance,

in Fig. 2 by the aid of condensers C". The chance of. insuring suchcapacitive equalization is a special advantage of the arrangement ofthis invention. For-when a push-pull amplifier involves inherentirregularities of an electrical nature, in other words, when due todissimilarities in the resonancecurves the push-pull transformer andbecause of dissimilarities of the tubes the amplifier curves aredifferent both as to amount and phase, such a capacity neutralization orcompensation is not practicable.

If it were feasibleto secure the conditions here inbe'fore describedinan absolute sense, then a perfectly non-regenerative push-pull amplifierscheme would be obtained. Although, as will be understood'the conditionsstipulated canbe fulfilled only to an approximate sense, it will beeasily understood that a neutralization of ohmic resistances can besecuredwith a far higher degree of accuracy or closeness than anequalization of transformers or inductance'coils, and'that as a resultthe quality of the amplifier here disclosed is far higher than that ofarrangements known in the prior art.' 7 a V 7 What is claimed is: 1 a VIn an amplification system, in'combination, two electron tubes eachhaving cathode, grid and plate electrodes, a source of power connectedto said'cathode electrodes, a pair of aperiodic input resistors, an.aperiodic output resistor, said input resistors being provided with amultiplicity of variable tap connections, two additional outputresistors, a source of plate potential, a plurality of condensers, abalanced network including certain of said'tap connections wherein saidcathode electrodes are connected together and to said in- .putresistors, said cathode electrodes being connected through said sourceof plate potentialto a variable. central tap on said output resistor,said grid electrodes being connected to certain of said taps on saidinputresistors on opposite sidesof saidcatho de taps, each'ofjsaid plateelectrodes being connected through one of said additional outputresistors to said output resistor, said two plates being connected toopposite sides of said output resistor through variable taps, inputconnections'including a transformer for said amplifying system connectedto certain of said variable input taps on said input' resistors throughtwo of "said condensers, output connections including a transformer forsaid amplifying system connected fto said output resistor onopposite'sides of said central tap, thereof through two other of said condensers,whereby the energy supplied to said input connections'is amplified anddelivered to said output connections substantially without distortion.

f FELIX STRECKER;

